Art of tuning magnetostrictive elements



June 17, 1947. A E LANE ART OF TUNING MAGNETOSTRICTIVE ELEMENTS Filed Nov. 29, 1944 .my ZJ AT TOR MY stares ortica ABT (VF TUNING MAGNE'EFSTRECTNE ELEMENTS Albert Edward Lane, Wenonah, N. L9 usata-nor to Radio Corporation of America, a corporation oi Delaware Application November 29, llglll, Serial No. 565,725 comme. (ci. 17a-12e) This invention relates to the art of tuning magnetostrictive elements and has special reference to the tuning of tubiform elements constituted oi nickel or equivalent (i. e. magnetic) material.

It is sometimes desirable to endow a magnetostrictive element with a frequency responsecharacteristic other than that dictated -by the physical dimensions of the element per se. To this end it has previously been proposed (see i'atent 942,897) to load a. magnetostrictive rod in a manner analogous to that commonly employed in tuning the reeds or tines oi a music boa, i. e. by soldering a weight to the free end of the rod with a view to altering the eective mass (and hence the frequency) thereof. The trouble with this prior art method of tuning a vibratile element resides not only in the fact 'that the auxiliary weight or load increases the over-all length of the element, but also in the fact that when applied to a bank of magnetostrictive elements it is usually necessary to employ some auxiliary support or centering means for the load on each element. Furthermore, since the Weight is soldered to the magnetostrictive element and is usually of a diameter greater than that of the coil which surrounds the said element it is exceedingly dilcult to replace a burnt-out coil.

Accordingly, the principal object of the present invention is to obviate the foregoing and other disadvantages of present day methods of and means for tuning a vibratile element of the general character described.

.Another and related object of the present invention is to provide an improved magnetostrictive unit, of any desired (xed) frequencycharacteristic, and one characterized by the simplicity and economy or" its parts, by its compact structure, and by its trouble-free performance.

c foregoing objects are achieved in accordance with the invention by providing a more or s conventional tubular magnetostrictive elenent with a tuning element in the form of a discrete re-entrant portion or plug of suitable mass and secured, in a novel manner, within the bore oi the tube in a position best calculated to the magnetostrictive element with the desired frequency response-characteristic.

:Certain preferred details of construction together with other objects and advantages will be apparent and the invention itself will be best understood by reference to the following specircation and to the accompanying drawing rherein:

iii

Fig. 1 is a longitudinal section of a. magnetostrictive tube, tuned in accordance with the invention and aixed to a metal diaphragm and Fig. 2 is an end view of the tuned tube of Fig. l..

In the drawing the invention is 'shown as applied to a typical underwater signaling system comprising a, metal diaphragm l (which may comprise either the skin of the vessel or a wall of a separate water-tight housing) to which a tubular magnetostrictive element 3 ls amxed by soldering or sweating one end of the tube Within a counter-sunk seat 5, provided for the purpose, in inner surface of the diaphragm l. The tubular magnetostrictive element 3 is surrounded throughout a portion of its length by a signal current carrying coil 'l which is wound on a iorm and supported on a suitable insulating frame l i above the surface of the diaphragm i. Usually the signaling system comprises a plurality or "bank of magnetostrictive elements Il and, in this case, a plate i3 for distributing the iiux from one or more polarizing magnets I5 may be mounted in a plane normal to the axis of the said elements. Since the flux distributing plate i3 must be mounted closely adjacent to the free end of the magnetostrictive element or elements it is apparent that the advantages of such a plate could not be realized in a signaling system wherein the magnetostrictive element 3 is tuned, as in the prior art, by a mass which extends beyond the end of the said element or elements.

As previously indicated the present invention obviates the foregoing and other objections to prior art tuning devices by the provision of a tuning element or load in the form of a. reentrant part or'plug lll of special design, which is mounted within the bore i@ of the magnetostrictive tube 3 adjacent to the free end thereof.

As clearly shown in Fig. l the tuning element il for the magnetostrictlve tube 3 comprises three integral sections ila, llb, llc, respectively. The outer section lla is of a diameter very slightly less than that of the inner diameter of the tube 3 so that it may be entered into the bore of the said tube and aiiixed to the inner surface thereof as by a compression force appliedto the outer surface of the tube, as indicated at 3d.A It will be observed that the outer end of the part ila of the plug ll is not flush with the outer end of the tube@ but terminates slightly short of the said end. Thus, should there be any inaccuracy in the length or the said tube, the said end portion of the tube may be ground down, without changing the mass of the plug il, to provide an air-gap of the desired length between the tube and the flux distributing plate i3.

Since the outer end portion lla of the plug is in contact with the inner surface of the tube 3 it serves not only to alter the natural frequency of the said element but also to dampen its vibrations to a limited degree, i. e. to the degree determined by the length of the said end portion.. Such a damping action is especially desirable in suppressing odd harmonics which, if propagated, might prove disturbing to installations operating at such higher frequencies. In most cases the described degree of damping is achieved when the length of the part ila corresponds substantially to the diameter of the bore I9 of the magnetostrictive tube 3. The intermediate portion l'lb of the plug, on the other hand, is of a diameter lessV than that of the bore i9 and, since it does not touch the inner surface of the tube, operates only (by reason of its mass) to alter the frequency of the said tube i3 and not to dampen its oscillations.

The inner end of the tuning element or plug il is preferably tapered, as indicated at llc, to receive a complementarily shaped tool (not shown) for centering the said plug prior to its attachment to the tube 3. The centering and, in most cases, the attachment, of the plug to the tube may take place prior to the attachment of the tube to the diaphragm i so that the said' tool may be inserted Within and withdrawn from the inner end of the tube.

One very real advantage of the present invention is that it permits the manufacturer of magnetostrictive signaling systems to employ magnetostrictive tubes of the same length and acacessories (supports-magnets, etc.) of a single size for signaling units designed to operate at diierent frequencies. Thus, should a manufacturer be called upon to produce a unit to operate at a frequency of say,.N kilocycles per second, he could employ an existing magnetostrictive unit having a different, higher frequency response and by the addition of a tuning element of the proper dimensions effect the desired alteration in frequency. Thus, a magnetostrictive element comprising a cold drawn seamless pure nickel tube having an overall length of L, an outside diameter of approximately L/6, wall thickness of approximately L/11 will, when inserted approximately L"/12 in a diaphragm, respond to a frequency of 2N kc. The same element when provided with a tuning element constituted of mat copper of the following dimensions and similar to the one (Il) shown in the drawing will tune the said 2N kc. tube to a frequency of N kc.

The dimensions of the tuning element in this case were approximately: outside diameter approximately L"/6, overall length approximately L"/2, length of head approximately L"/5.6l diameter of shank approximately L/7.5, length of shank approximately L/3.8, length of tapered end approximately L"/l5, angle of taper 30, weight 1.2.1 grams.

Various other modifications and applications of the invention will suggest themselves to those skilled in the art. Accordingly, the foregoing should be interpreted as illustrative and not in a limiting sense except as required by the prior art and by the spirit of the appended claims.

I claim:

1. -'I'he combination with a tubular magnetostrictive element having a fixed-end and a freeend and dimensioned to respond to a certain fundamental frequency, of a nonmagnetic member secured to the interior of said tubular element adjacent to the said free-end thereof, said nonmagnetic member comprising a body porn tion of a length corresponding substantiallyv to the inner diameter of said tubular element and a concentric dependent portion of a diameter less than that of said body portion.

2. The invention as set forth in claim 1 and wherein said free-end of said tubular magnetostrictive element extends slightly beyond the adjacent end of said body portion of said nonmagnetic member.

3. In combination; a magnetostrictive tube having a bore of substantially uniform diameter, and a tuning element for said tube comprising a head portion constituted of non-magnetic material seated within the bore of said tube and a dependent frequency determining portion of a diameter substantially less than that of said bore extending into said tube.

ALBERT EDWARD LANE.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 942,897 Garrett et al Dec. 14, 1909 1,882,398 Pierce Oct. 11, 1932 2,076,330 Wood et al. 1 Apr. 6, 1937 2,063,950 Steinberger Dec. 15, 1936 FOREIGN PATENTS Number Country Date 832,891 France Oct. 4, 1938 

